1. Field of the Invention
The present invention relates to an image processing apparatus which detects a lesion in a body cavity image (or digestive organ image) captured in an inside of a living body, an image processing method, and a computer program product.
2. Description of the Related Art
Conventionally, as a processing of detecting a lesion with respect to a body cavity image captured in an inside of a living body, a technique of dividing the image into blocks, calculating color information of each block, and comparing a reference value for color information of a known lesion such as a bleeding site with a reference value for color information of a healthy tissue has been disclosed in Japanese translation No. 2004-521693 of PCT international application.
In addition, a technique of detecting a focal shadow (or calcification masses) with respect to a medical image has been known, for example, in Japanese Patent Application Laid-Open No. 2002-325762. In the technique presented herein, an image is scanned in sequence and an average of image values in a small region in which a pixel of interest is located in the center thereof is obtained for detecting a candidate focal shadow. A border of the candidate focal shadow is detected by categorizing each pixel in the small region into one of two groups depending on whether the pixel is larger or smaller than the average of the image values in the small region, obtaining an average of coordinate positions of pixels categorized into each one of the two groups, and extracting a place where a difference in distance among the coordinate positions is present. Thereafter, whether or not the region is a shadow caused by a focus is identified depending on a manner of a pixel value change in pixels lying between a pixel in the candidate focal shadow region and a pixel outside the region.
In Japanese Patent Application Laid-Open No. 2002-325762, a detection of a focal shadow by using the Quoit filter is disclosed as a conventional technique. The Quoit filter is formed by a circular filter and a ring filter surrounding the circular filter. When each pixel of an image is scanned by the Quoit filter, the circular filter shows a large value in a region where a luminance locally rises while the ring filter shows a small value. This enables a detection of a focus whose luminance is locally high.